This invention pertains to a process for cracking lignin-containing feed materials in a fast fluidized bed reaction zone operating at high gas velocities and low residence times to produce useful aromatic and paraffinic hydrocarbon products and olefins such as ethylene.
Lignin is a by-product of wood pulping operations, and is currently utilized as a fuel in modern paper mill practice. Chemically, lignin can be considered as a three dimensional condensation product of coniferyl, p-coumaryl and sinapyl alcohols. While coniferyl alcohol is dominant, the ratios of the three alcohols depend on the type of wood used. Hardwoods have more sinapyl alcohol. Some technologists symbolize the coniferyl building unit of lignin as R-C-C-C, in which R represents the 4-hydroxy-3-methoxy phenyl group, which is also referred to as the guaiacyl group. Lignin is a major constituent in a principal by-product stream from paper mills, usually called "black liquor". If desired, lignin-like material can be precipitated from black liquor by salting out, by changes of pH value, and by the addition of certain cations.
Various methods for conversion of lignin and lignocellulose materials to produce fuel gas and chemicals have been previously disclosed, including U.S. Pat. No. 4,164,397 to Hunt et al, which uses a downflow stirred reactor, U.S. Pat. No. 4,166,830 to Guth et al which discloses a cracking process in multiple reactors at high velocities using atomizing nozzles. A process for cracking petroleum feedstocks to produce ethylene in an elongated reactor at short residence times not exceeding about 2 seconds is disclosed in U.S. Pat. No. 4,061,562 to McKinney. Also, the gasification of coal using a fluidized bed of char particles at high superficial gas velocity is disclosed by U.S. Pat. Nos. 3,840,353, 3,957,457, and 3,957,458 to Squires. However, reactions utilizing fast fluidized bed contacting techniques have apparently not previously been used for thermally cracking lignin-containing feedstocks to control reaction time and produce desirable aromatic chemical products. The fast fluidized bed contacting regime has been found especially useful in controlling cracking severity and limiting residence times.